This invention relates to entry structures and more particularly to an entry structure having an air-operated door lock.
Many commercial and public buildings, such as large office buildings, schools, and the like, are used primarily during business hours and afterwards are locked to prevent unauthorized entry. To reduce the cost of security, it is desireable to have the locks on the exterior doors of these buildings operated remotely from a single location. The same is true of the locks on interior doors at critical locations within the buildings.
Doors formed primarily of glass are found quite commonly in large commercial and public buildings, and doors of this nature usually have extruded aluminum rails surrounding and supporting the glass. One of the rails usually contains a lock, the bolt of which projects into a keeper on a door frame or on another door. Locks of this nature are in most instances operated at the door by a key and when so operated project a dead bolt into the keeper.
Attempts have been made to operate such locks electrically, but this usually requires high voltages and currents in the circuitry leading to the lock. Many building codes, however, place severe limitations on the amount of electrical power that may be transmitted through a door. For example, Underwriters Laboratories will not approve any door mounted appliance which requires more than 100 volt-amperes. Moreover, if the electrically operated locks utilize a screw to move the bolt, as is sometimes the case, an electrical failure will leave the lock in the position it was at the time of the failure, since screw-type drive mechanisms are not reversible. This may create a safety hazard, assuming the electrical failure occurs when the bolt is projected into its keeper.